1. Field of the Invention
This invention relates to novel high-strength cement-containing ceramic articles decreased in or prevented from efforescence and a method for production thereof. The articles consist essentially of inorganic hydraulic cement such as portland cement, and heat-vitrifiable inorganic powder, as well as silicate mineral powder such as magnesium silicate minerals and/or aluminum silicate minerals. The ceramic articles according to the present invention are substantially prevented from efflorescence caused by the vitrifiable component and cement component, has large frost resistance, and is often increased in strength by the side effect of the silicate mineral component contained therein. Incidentally, the moldability and shape retention of green molded articles as well as the shrinkage and deformation of the articles in the course of firing are markedly improved due to the hydraulic cement component contained therein. The present ceramic articles are, for example, useful for building parts or materials.
2. Prior Art
Conventional pottery or porcelain articles have been produced by molding clay materials and firing the molded articles. However, there have been many problems in the moldability and in shape retention of the green molded articles, and in shrinkage and deformation during the course of firing. These problems have been considered unavoidable.
In the course of research, the present inventors have developed a method which comprises molding an aqueous blend containing hydraulic cement, aggregate and a vitrifiable component such as glass powder and containing no silicate mineral powder mentioned above; substantially hydrating the cement component; and then firing the molded article to a temperature of 900.degree. C. or more. Efflorescence due to the glass powder and cement component, however, markedly appeared on the surfaces of the resulting articles in an amount of about 20 to 50% of the whole surface area of the article. It was also desired to further increase the strength of the articles
A method has been known for producing a cement concrete article (e.g. Laid-open European Patent Application No. 80303696.1, which comprises molding an aqueous blend of hydraulic cement, aggregate and preferably a calcium compound, hydrating the molded article, firing the hydrated article at a temperature lower than 900.degree. C., and then rehydrating the fired article. The ceramic article of the present invention, however, is quite different from such rehydrated concrete articles in strength, components and operations; the bending strength of such concrete articles being about 13 MPa. Moreover, it is noted that the inefficient step of rehydration mentioned above is not needed in the present invention.